Interchangeable Jig-Saw Puzzles

A range of three puzzles listed below where groups of pieces from each figure can be freely interchanged. Unlike the "Changing Picture" range which have two solutions there are many different ways in which the interchangeable puzzles can be assembled.

The Mad Tea-Party (illustrated)
The Bruin Boys
Cook and her Policeman

They were introduced in the mid 1930's and more comprehensive information can be read in Chapter 29 of Brian Sulman's book on Salmon Jigsaw Puzzles.